Add experimental ring buffer implementation.

research/README.txt

+This folder contains code that I'm experimenting with outside of the main mini_al library. It's just for
+my own research and experimenting which I'm putting into the repository for version control purposes and
+to get feedback from the community. You should not consider any of this code to be production quality.
\ No newline at end of file

research/mal_ring_buffer.h

+// Consider this code public domain.
+//
+// This is some research into a ring buffer implementation. Requirements:
+// - Lock free (assuming single producer, single consumer)
+// - Support for interleaved and deinterleaved streams
+// - Must allow the caller to allocate their own block of memory
+//   - Buffers allocated internally must be aligned to MAL_SIMD_ALIGNMENT
+
+// USAGE
+//
+// - Call mal_rb_init() to initialize a simple buffer, with an optional pre-allocated buffer. If you pass in NULL
+//   for the pre-allocated buffer, it will be allocated for you and free()'d in mal_rb_uninit(). If you pass in
+//   your own pre-allocated buffer, free()-ing is left to you.
+//
+// - Call mal_rb_init_ex() if you need a deinterleaved buffer. The data for each sub-buffer is offset from each
+//   other based on the stride. Use mal_rb_get_subbuffer_stride(), mal_rb_get_subbuffer_offset() and
+//   mal_rb_get_subbuffer_ptr() to manage your sub-buffers.
+//
+// - Use mal_rb_acquire_read() and mal_rb_acquire_write() to retrieve a pointer to a section of the ring buffer.
+//   You specify the number of bytes you need, and on output it will set to what was actually acquired. If the
+//   read or write pointer is positioned such that the number of bytes requested will require a loop, it will be
+//   clamped to the end of the buffer. Therefore, the number of bytes you're given may be less than the number
+//   you requested.
+//
+// - After calling mal_rb_acquire_read/write(), you do your work on the buffer and then "commit" it with
+//   mal_rb_commit_read/write(). This is where the read/write pointers are updated. When you commit you need to
+//   pass in the buffer that was returned by the earlier call to mal_rb_acquire_read/write() and is only used
+//   for validation. The number of bytes passed to mal_rb_commit_read/write() is what's used to increment the
+//   pointers.
+//
+// - If you want to correct for drift between the write pointer and the read pointer you can use a combination
+//   of mal_rb_pointer_distance(), mal_rb_seek_read() and mal_rb_seek_write(). Note that you can only move the
+//   pointers forward, and you should only move the read pointer forward via the consumer thread, and the write
+//   pointer forward by the producer thread. If there is too much space between the pointers, move the read
+//   pointer forward. If there is too little space between the pointers, move the write pointer forward.
+
+// NOTES
+//
+// - Probably buggy.
+// - Still experimenting with the API. Open to suggestions.
+// - Thread safety depends on a single producer, single consumer model. Only one thread is allowed to write, and
+//   only one thread is allowed to read. The producer is the only one allowed to move the write pointer, and the
+//   consumer is the only one allowed to move the read pointer.
+// - Thread safety not fully tested - may even be completely broken.
+// - Operates on bytes. May end up adding to higher level helpers for doing everything per audio frame.
+// - Maximum buffer size is 0x7FFFFFFF-(MAL_SIMD_ALIGNMENT-1) because of reasons.
+
+#ifndef mal_ring_buffer_h
+#define mal_ring_buffer_h
+
+typedef struct
+{
+    void* pBuffer;
+    mal_uint32 subbufferSizeInBytes;
+    mal_uint32 subbufferCount;
+    mal_uint32 subbufferStrideInBytes;
+    mal_uint32 readOffset;              /* Most significant bit is the loop flag. Lower 31 bits contains the actual offset in bytes. */
+    mal_uint32 writeOffset;             /* Most significant bit is the loop flag. Lower 31 bits contains the actual offset in bytes. */
+    mal_bool32 ownsBuffer          : 1; /* Used to know whether or not mini_al is responsible for free()-ing the buffer. */
+    mal_bool32 clearOnWriteAcquire : 1; /* When set, clears the acquired write buffer before returning from mal_rb_acquire_write(). */
+} mal_rb;
+
+mal_result mal_rb_init_ex(size_t subbufferSizeInBytes, size_t subbufferCount, size_t subbufferStrideInBytes, void* pOptionalPreallocatedBuffer, mal_rb* pRB);
+mal_result mal_rb_init(size_t bufferSizeInBytes, void* pOptionalPreallocatedBuffer, mal_rb* pRB);
+void mal_rb_uninit(mal_rb* pRB);
+mal_result mal_rb_acquire_read(mal_rb* pRB, size_t* pSizeInBytes, void** ppBufferOut);
+mal_result mal_rb_commit_read(mal_rb* pRB, size_t sizeInBytes, void* pBufferOut);
+mal_result mal_rb_acquire_write(mal_rb* pRB, size_t* pSizeInBytes, void** ppBufferOut);
+mal_result mal_rb_commit_write(mal_rb* pRB, size_t sizeInBytes, void* pBufferOut);
+mal_result mal_rb_seek_read(mal_rb* pRB, size_t offsetInBytes);
+mal_result mal_rb_seek_write(mal_rb* pRB, size_t offsetInBytes);
+mal_int32 mal_rb_pointer_distance(mal_rb* pRB);    /* Returns the distance between the write pointer and the read pointer. Should never be negative for a correct program. */
+size_t mal_rb_get_subbuffer_stride(mal_rb* pRB);
+size_t mal_rb_get_subbuffer_offset(mal_rb* pRB, size_t subbufferIndex);
+void* mal_rb_get_subbuffer_ptr(mal_rb* pRB, size_t subbufferIndex, void* pBuffer);
+
+#endif  // mal_ring_buffer_h
+
+#ifdef MINI_AL_IMPLEMENTATION
+void* mal_rb__get_read_ptr(mal_rb* pRB)
+{
+    mal_assert(pRB != NULL);
+    return mal_offset_ptr(pRB->pBuffer, (pRB->readOffset & 0x7FFFFFFF));
+}
+
+void* mal_rb__get_write_ptr(mal_rb* pRB)
+{
+    mal_assert(pRB != NULL);
+    return mal_offset_ptr(pRB->pBuffer, (pRB->writeOffset & 0x7FFFFFFF));
+}
+
+mal_uint32 mal_rb__construct_offset(mal_uint32 offsetInBytes, mal_uint32 offsetLoopFlag)
+{
+    return offsetLoopFlag | offsetInBytes;
+}
+
+void mal_rb__deconstruct_offset(mal_uint32 offset, mal_uint32* pOffsetInBytes, mal_uint32* pOffsetLoopFlag)
+{
+    mal_assert(pOffsetInBytes != NULL);
+    mal_assert(pOffsetLoopFlag != NULL);
+
+    *pOffsetInBytes  = offset & 0x7FFFFFFF;
+    *pOffsetLoopFlag = offset & 0x80000000;
+}
+
+
+mal_result mal_rb_init_ex(size_t subbufferSizeInBytes, size_t subbufferCount, size_t subbufferStrideInBytes, void* pOptionalPreallocatedBuffer, mal_rb* pRB)
+{
+    if (pRB == NULL) {
+        return MAL_INVALID_ARGS;
+    }
+
+    if (subbufferSizeInBytes == 0 || subbufferCount == 0) {
+        return MAL_INVALID_ARGS;
+    }
+
+    const mal_uint32 maxSubBufferSize = 0x7FFFFFFF - (MAL_SIMD_ALIGNMENT-1);
+    if (subbufferSizeInBytes > maxSubBufferSize) {
+        return MAL_INVALID_ARGS;    // Maximum buffer size is ~2GB. The most significant bit is a flag for use internally.
+    }
+
+
+    mal_zero_object(pRB);
+    pRB->subbufferSizeInBytes = (mal_uint32)subbufferSizeInBytes;
+    pRB->subbufferCount = (mal_uint32)subbufferCount;
+
+    if (pOptionalPreallocatedBuffer != NULL) {
+        pRB->subbufferStrideInBytes = (mal_uint32)subbufferStrideInBytes;
+        pRB->pBuffer = pOptionalPreallocatedBuffer;
+    } else {
+        // Here is where we allocate our own buffer. We always want to align this to MAL_SIMD_ALIGNMENT for future SIMD optimization opportunity. To do this
+        // we need to make sure the stride is a multiple of MAL_SIMD_ALIGNMENT.
+        pRB->subbufferStrideInBytes = (pRB->subbufferSizeInBytes + (MAL_SIMD_ALIGNMENT-1)) & ~MAL_SIMD_ALIGNMENT;
+
+        size_t bufferSizeInBytes = (size_t)pRB->subbufferCount*pRB->subbufferStrideInBytes;
+        pRB->pBuffer = mal_aligned_malloc(bufferSizeInBytes, MAL_SIMD_ALIGNMENT);
+        if (pRB->pBuffer == NULL) {
+            return MAL_OUT_OF_MEMORY;
+        }
+
+        mal_zero_memory(pRB->pBuffer, bufferSizeInBytes);
+        pRB->ownsBuffer = MAL_TRUE;
+    }
+
+    return MAL_SUCCESS;
+}
+
+mal_result mal_rb_init(size_t bufferSizeInBytes, void* pOptionalPreallocatedBuffer, mal_rb* pRB)
+{
+    return mal_rb_init_ex(bufferSizeInBytes, 1, 0, pOptionalPreallocatedBuffer, pRB);
+}
+
+void mal_rb_uninit(mal_rb* pRB)
+{
+    if (pRB == NULL) {
+        return;
+    }
+
+    if (pRB->ownsBuffer) {
+        mal_free(pRB->pBuffer);
+    }
+}
+
+mal_result mal_rb_acquire_read(mal_rb* pRB, size_t* pSizeInBytes, void** ppBufferOut)
+{
+    if (pRB == NULL || pSizeInBytes == NULL || ppBufferOut == NULL) {
+        return MAL_INVALID_ARGS;
+    }
+
+    // The returned buffer should never move ahead of the write pointer.
+    mal_uint32 writeOffsetInBytes;
+    mal_uint32 writeOffsetLoopFlag;
+    mal_rb__deconstruct_offset(pRB->writeOffset, &writeOffsetInBytes, &writeOffsetLoopFlag);
+
+    mal_uint32 readOffsetInBytes;
+    mal_uint32 readOffsetLoopFlag;
+    mal_rb__deconstruct_offset(pRB->readOffset, &readOffsetInBytes, &readOffsetLoopFlag);
+
+    // The number of bytes available depends on whether or not the read and write pointers are on the same loop iteration. If so, we
+    // can only read up to the write pointer. If not, we can only read up to the end of the buffer.
+    size_t bytesAvailable;
+    if (readOffsetLoopFlag == writeOffsetLoopFlag) {
+        bytesAvailable = writeOffsetInBytes - readOffsetInBytes;
+    } else {
+        bytesAvailable = pRB->subbufferSizeInBytes - readOffsetInBytes;
+    }
+
+    size_t bytesRequested = *pSizeInBytes;
+    if (bytesRequested > bytesAvailable) {
+        bytesRequested = bytesAvailable;
+    }
+
+    *pSizeInBytes = bytesRequested;
+    (*ppBufferOut) = mal_rb__get_read_ptr(pRB);
+
+    return MAL_SUCCESS;
+}
+
+mal_result mal_rb_commit_read(mal_rb* pRB, size_t sizeInBytes, void* pBufferOut)
+{
+    if (pRB == NULL) {
+        return MAL_INVALID_ARGS;
+    }
+
+    // Validate the buffer.
+    if (pBufferOut != mal_rb__get_read_ptr(pRB)) {
+        return MAL_INVALID_ARGS;
+    }
+
+    mal_uint32 readOffsetInBytes;
+    mal_uint32 readOffsetLoopFlag;
+    mal_rb__deconstruct_offset(pRB->readOffset, &readOffsetInBytes, &readOffsetLoopFlag);
+
+    // Check that sizeInBytes is correct. It should never go beyond the end of the buffer.
+    mal_uint32 newReadOffsetInBytes = (mal_uint32)(readOffsetInBytes + sizeInBytes);
+    if (newReadOffsetInBytes > pRB->subbufferSizeInBytes) {
+        return MAL_INVALID_ARGS;    // <-- sizeInBytes will cause the read offset to overflow.
+    }
+
+    // Move the read pointer back to the start if necessary.
+    mal_uint32 newReadOffsetLoopFlag = readOffsetLoopFlag;
+    if (newReadOffsetInBytes == pRB->subbufferSizeInBytes) {
+        newReadOffsetInBytes = 0;
+        newReadOffsetLoopFlag ^= 0x80000000;
+    }
+
+    mal_atomic_exchange_32(&pRB->readOffset, mal_rb__construct_offset(newReadOffsetLoopFlag, newReadOffsetInBytes));
+    return MAL_SUCCESS;
+}
+
+mal_result mal_rb_acquire_write(mal_rb* pRB, size_t* pSizeInBytes, void** ppBufferOut)
+{
+    if (pRB == NULL || pSizeInBytes == NULL || ppBufferOut == NULL) {
+        return MAL_INVALID_ARGS;
+    }
+
+    // The returned buffer should never overtake the read buffer.
+    mal_uint32 readOffsetInBytes;
+    mal_uint32 readOffsetLoopFlag;
+    mal_rb__deconstruct_offset(pRB->readOffset, &readOffsetInBytes, &readOffsetLoopFlag);
+
+    mal_uint32 writeOffsetInBytes;
+    mal_uint32 writeOffsetLoopFlag;
+    mal_rb__deconstruct_offset(pRB->writeOffset, &writeOffsetInBytes, &writeOffsetLoopFlag);
+
+    // In the case of writing, if the write pointer and the read pointer are on the same loop iteration we can only
+    // write up to the end of the buffer. Otherwise we can only write up to the read pointer. The write pointer should
+    // never overtake the read pointer.
+    size_t bytesAvailable;
+    if (writeOffsetLoopFlag == readOffsetLoopFlag) {
+        bytesAvailable = pRB->subbufferSizeInBytes - writeOffsetInBytes;
+    } else {
+        bytesAvailable = readOffsetInBytes - writeOffsetInBytes;
+    }
+
+    size_t bytesRequested = *pSizeInBytes;
+    if (bytesRequested > bytesAvailable) {
+        bytesRequested = bytesAvailable;
+    }
+
+    *pSizeInBytes = bytesRequested;
+    *ppBufferOut  = mal_rb__get_write_ptr(pRB);
+
+    // Clear the buffer if desired.
+    if (pRB->clearOnWriteAcquire) {
+        mal_zero_memory(*ppBufferOut, *pSizeInBytes);
+    }
+
+    return MAL_SUCCESS;
+}
+
+mal_result mal_rb_commit_write(mal_rb* pRB, size_t sizeInBytes, void* pBufferOut)
+{
+    if (pRB == NULL) {
+        return MAL_INVALID_ARGS;
+    }
+
+    // Validate the buffer.
+    if (pBufferOut != mal_rb__get_write_ptr(pRB)) {
+        return MAL_INVALID_ARGS;
+    }
+
+    mal_uint32 writeOffsetInBytes;
+    mal_uint32 writeOffsetLoopFlag;
+    mal_rb__deconstruct_offset(pRB->writeOffset, &writeOffsetInBytes, &writeOffsetLoopFlag);
+
+    // Check that sizeInBytes is correct. It should never go beyond the end of the buffer.
+    mal_uint32 newWriteOffsetInBytes = (mal_uint32)(writeOffsetInBytes + sizeInBytes);
+    if (newWriteOffsetInBytes > pRB->subbufferSizeInBytes) {
+        return MAL_INVALID_ARGS;    // <-- sizeInBytes will cause the read offset to overflow.
+    }
+
+    // Move the read pointer back to the start if necessary.
+    mal_uint32 newWriteOffsetLoopFlag = writeOffsetLoopFlag;
+    if (newWriteOffsetInBytes == pRB->subbufferSizeInBytes) {
+        newWriteOffsetInBytes = 0;
+        newWriteOffsetLoopFlag ^= 0x80000000;
+    }
+
+    mal_atomic_exchange_32(&pRB->writeOffset, mal_rb__construct_offset(newWriteOffsetLoopFlag, newWriteOffsetInBytes));
+    return MAL_SUCCESS;
+}
+
+mal_result mal_rb_seek_read(mal_rb* pRB, size_t offsetInBytes)
+{
+    if (pRB == NULL || offsetInBytes > pRB->subbufferSizeInBytes) {
+        return MAL_INVALID_ARGS;
+    }
+
+    mal_uint32 readOffsetInBytes;
+    mal_uint32 readOffsetLoopFlag;
+    mal_rb__deconstruct_offset(pRB->readOffset, &readOffsetInBytes, &readOffsetLoopFlag);
+
+    mal_uint32 writeOffsetInBytes;
+    mal_uint32 writeOffsetLoopFlag;
+    mal_rb__deconstruct_offset(pRB->writeOffset, &writeOffsetInBytes, &writeOffsetLoopFlag);
+
+    mal_uint32 newReadOffsetInBytes = readOffsetInBytes;
+    mal_uint32 newReadOffsetLoopFlag = readOffsetLoopFlag;
+
+    // We cannot go past the write buffer.
+    if (readOffsetLoopFlag == writeOffsetLoopFlag) {
+        if ((readOffsetInBytes + offsetInBytes) > writeOffsetInBytes) {
+            newReadOffsetInBytes = writeOffsetInBytes;
+        } else {
+            newReadOffsetInBytes = (readOffsetInBytes + offsetInBytes);
+        }
+    } else {
+        // May end up looping.
+        if ((readOffsetInBytes + offsetInBytes) >= pRB->subbufferSizeInBytes) {
+            newReadOffsetInBytes = (readOffsetInBytes + offsetInBytes) - pRB->subbufferSizeInBytes;
+            newReadOffsetLoopFlag ^= 0x80000000;    /* <-- Looped. */
+        } else {
+            newReadOffsetInBytes = (readOffsetInBytes + offsetInBytes);
+        }
+    }
+
+    mal_atomic_exchange_32(&pRB->readOffset, mal_rb__construct_offset(newReadOffsetInBytes, newReadOffsetLoopFlag));
+    return MAL_SUCCESS;
+}
+
+mal_result mal_rb_seek_write(mal_rb* pRB, size_t offsetInBytes)
+{
+    if (pRB == NULL) {
+        return MAL_INVALID_ARGS;
+    }
+
+    mal_uint32 readOffsetInBytes;
+    mal_uint32 readOffsetLoopFlag;
+    mal_rb__deconstruct_offset(pRB->readOffset, &readOffsetInBytes, &readOffsetLoopFlag);
+
+    mal_uint32 writeOffsetInBytes;
+    mal_uint32 writeOffsetLoopFlag;
+    mal_rb__deconstruct_offset(pRB->writeOffset, &writeOffsetInBytes, &writeOffsetLoopFlag);
+
+    mal_uint32 newWriteOffsetInBytes = writeOffsetInBytes;
+    mal_uint32 newWriteOffsetLoopFlag = writeOffsetLoopFlag;
+
+    // We cannot go past the write buffer.
+    if (readOffsetLoopFlag == writeOffsetLoopFlag) {
+        // May end up looping.
+        if ((writeOffsetInBytes + offsetInBytes) >= pRB->subbufferSizeInBytes) {
+            newWriteOffsetInBytes = (writeOffsetInBytes + offsetInBytes) - pRB->subbufferSizeInBytes;
+            newWriteOffsetLoopFlag ^= 0x80000000;    /* <-- Looped. */
+        } else {
+            newWriteOffsetInBytes = (writeOffsetInBytes + offsetInBytes);
+        }
+    } else {
+        if ((writeOffsetInBytes + offsetInBytes) > readOffsetInBytes) {
+            newWriteOffsetInBytes = readOffsetInBytes;
+        } else {
+            newWriteOffsetInBytes = (writeOffsetInBytes + offsetInBytes);
+        }
+    }
+
+    mal_atomic_exchange_32(&pRB->writeOffset, mal_rb__construct_offset(newWriteOffsetInBytes, newWriteOffsetLoopFlag));
+    return MAL_SUCCESS;
+}
+
+mal_int32 mal_rb_pointer_distance(mal_rb* pRB)
+{
+    if (pRB == NULL) {
+        return 0;
+    }
+
+    mal_uint32 readOffsetInBytes;
+    mal_uint32 readOffsetLoopFlag;
+    mal_rb__deconstruct_offset(pRB->readOffset, &readOffsetInBytes, &readOffsetLoopFlag);
+
+    mal_uint32 writeOffsetInBytes;
+    mal_uint32 writeOffsetLoopFlag;
+    mal_rb__deconstruct_offset(pRB->writeOffset, &writeOffsetInBytes, &writeOffsetLoopFlag);
+
+    if (readOffsetLoopFlag == writeOffsetLoopFlag) {
+        return writeOffsetInBytes - readOffsetInBytes;
+    } else {
+        return writeOffsetInBytes + (pRB->subbufferSizeInBytes - readOffsetInBytes);
+    }
+}
+
+size_t mal_rb_get_subbuffer_stride(mal_rb* pRB)
+{
+    if (pRB == NULL) {
+        return 0;
+    }
+
+    if (pRB->subbufferStrideInBytes == 0) {
+        return (size_t)pRB->subbufferSizeInBytes;
+    }
+
+    return (size_t)pRB->subbufferStrideInBytes;
+}
+
+size_t mal_rb_get_subbuffer_offset(mal_rb* pRB, size_t subbufferIndex)
+{
+    if (pRB == NULL) {
+        return 0;
+    }
+
+    return subbufferIndex * mal_rb_get_subbuffer_stride(pRB);
+}
+
+void* mal_rb_get_subbuffer_ptr(mal_rb* pRB, size_t subbufferIndex, void* pBuffer)
+{
+    if (pRB == NULL) {
+        return NULL;
+    }
+
+    return mal_offset_ptr(pBuffer, mal_rb_get_subbuffer_offset(pRB, subbufferIndex));
+}
+#endif  // MINI_AL_IMPLEMENTATION